1. Field of the Invention
The present invention relates to an improvement in a slip ring used, for example, in case that signals put out from various switches mounted on a steering wheel of a vehicle are transmitted to loads of a fixed type.
2. Description of the Prior Art
In the switches mounted on the steering wheel of the vehicle the slip ring has conventionally been used for electrical connections between the various switches mounted on a switch pad of a central portion of the steering wheel and the loads. In the prior art, for example, the slip ring has a structure shown in FIGS. 1 and 2. The slip ring consists substantially of a fixed member B provided therein co-axially in its radial direction with a few fixed contacts, for example, three fixed contacts A.sub.1, A.sub.2 and A.sub.3 of three lanes formed with an outermost lane, a middle lane, or central lane, and an innermost lane, the fixed member B being fixed to the vehicle body, and a case C fixed to the steering wheel and provided with the same number of movable contacts opposed to the fixed contacts, for example, three movable contacts D.sub.1, D.sub.2 and D.sub.3 respectively consisting of conductive plane springs and contacts, as shown in FIGS. 1 and 2. The case C can be rotated together with the steering wheel so that the movable contacts D.sub.1 to D.sub.3 are slidably brought into contact with the fixed contacts A.sub.1 to A.sub.3, respectively and thereby the signals put out from the switches can always be transmitted to the loads. However, in case that various switches are mounted on the steering wheel besides a horn switch whereby the signals are transmitted directly to the loads, both the number of the lanes having the fixed contacts and the number of the lanes having the movable contacts must be increased respectively in accordance with an increase in the mumber cf the switches.
However, if the number of the lanes is increased, the slip ring itself must be enlarged in its radial direction, but the slip ring has been provided with only three lanes at most in the prior art because the places or spaces where a steering column, the steering wheel and the like are mounted must necessarily be of a limited size, which results in that the number of the switches to be mounted on the steering wheel can not be increased.
In addition, a PCM electrical transmission system is used for transmission of the signals put out from many switches in the prior slip ring. However, if this system is adopted, a circuit portion must also be provided in the system therefor, which causes the increase of manufacturing cost.